1. Field of the Invention
The present invention relates to an optical microscope and a spectrum measuring method, and more particularly to an optical microscope detecting light of a wavelength different from that of laser light applied to a sample, and a spectrum measuring method.
2. Description of Related Art
Raman spectroscopy is advantageous in that measurement can be executed on samples of any form, for example, a gaseous form, a liquid form, a crystal form, and an amorphous solid form, irrespective of whether temperature is low or high, without using a special measurement atmosphere such as a vacuum atmosphere. In addition, the Raman spectroscopy is advantageous in that pretreatment of the sample can be omitted, and the sample can be measured as it is. Therefore, various measurements have been carried out utilizing these advantages. The application of the Raman spectroscopy enables measurement of molecules without staining, and measurement of impurities in a semiconductor.
To carry out the Raman spectroscopy, a Raman microscope using a spectroscope is disclosed (Japanese Unexamined Patent Publication Nos. 2002-14043 and 2003-344776). The Raman microscope focuses laser light to a sample. Then, the spectroscope diffuses Raman scattered light from the sample to thereby observe Raman spectrum. Further, the Raman microscope executes measurement while moving the sample to thereby measure spatial distribution of an intensity of Raman scattered light with a predetermined wavelength. There is disclosed another Raman microscope that illuminates a sample in a line form by use of a cylindrical lens for shortening measurement period to detect Raman scattered light with a CCD camera (CHARLENE A. DRUMM and another “Microscopic Raman Line-Imaging With Principal Component Analysis” APPLIED SPECTROSCOPY, 1995, vol. 49, No. 9, pp. 1331-1337). This Raman microscope illuminates the sample in the line form and thus, a large area can be illuminated at a time, and a measurement period can be shortened.
However, in the Raman microscope described in CHARLENE A. DRUMM and another “Microscopic Raman Line-Imaging With Principal Component Analysis” APPLIED SPECTROSCOPY, 1995, vol. 49, No. 9, pp. 1331-1337, laser light is changed into linear light by the cylindrical lens, resulting in a problem in that the sample cannot be uniformly illuminated. That is, a distribution of laser beam intensity along beam cross-section is generally similar to the Gaussian function, so its distribution is such that the intensity is highest at the center, and is decreased toward the edge of the laser spot. It is difficult to change the laser light into a linear light beam having uniform intensity. There is another problem in that a speckle noise occurs and hinders high-accuracy observation. That is, if a sample is illuminated by highly coherent laser light, the light is scattered due to dust and the like in an optical path. This scattered light leads to illumination unevenness (speckle noise) in an illuminated portion due to interference. As mentioned above, the conventional Raman microscope has a problem in that high-accuracy measurement is difficult. Further, the conventional Raman microscope faces a problem in that it is difficult to realize both of a shorter measure period and high-accuracy measurement.